中科大操作系统原理与实现课件3_Processes1.pdf

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1、操作系统原理与设计第3章Processes（进程）2陈香兰中国科学技术大学计算机学院2009年09月01日......提纲ProcessSchedulingProcessSchedulingQueuesSchedulersContextSwitchOperationonprocessesProcessCreationProcessTermination小结和作业......OutlineProcessSchedulingProcessSchedulingQueuesSchedulersContextSwitchOperationonprocessesProcess

2、CreationProcessTermination小结和作业......ProcessSchedulingTheobjectiveofmultiprogramming:???Theobjectiveoftimesharing:???Whatthesystemneed?theprocessschedulerselectsanavailableprocesstoexecuteontheCPU.......ProcessSchedulingTheobjectiveofmultiprogramming:???Theobjectiveoftimesharing:???Wh

3、atthesystemneed?theprocessschedulerselectsanavailableprocesstoexecuteontheCPU.......ProcessSchedulingQueuesProcessesmigrateamongthevariousqueuesIJobqueue–setofallprocessesinthesystemIReadyqueue–setofallprocessesresidinginmainmemory,readyandwaitingtoexecuteIDevicequeues–setofprocessesw

4、aitingforanI/Odevice......ReadyQueueAndVariousI/ODeviceQueues......RepresentationofProcessSchedulingIaqueueingdiagram......OutlineProcessSchedulingProcessSchedulingQueuesSchedulersContextSwitchOperationonprocessesProcessCreationProcessTermination小结和作业......SchedulersILong-termschedule

5、r(orjobscheduler)IselectswhichprocessesshouldbebroughtintothereadyqueueShort-termscheduler(orCPUscheduler)IselectswhichprocessshouldbeexecutednextandallocatesCPU......Theprimarydistinctionbetweenlong-term&short-termschedulersIITheprimarydistinctionbetweenlong-term&short-termschedulers

6、liesinfrequencyofexecutionIShort-termschedulerisinvokedveryfrequently(UNIT:ms)￿(mustbefast)ILong-termschedulerisinvokedveryinfrequently(UNIT:seconds,minutes)￿(maybeslow)IWHY?IThelong-termschedulercontrolsthedegreeofmultiprogrammingIthenumberofprocessesinmemory.Istable?......Theprimary

7、distinctionbetweenlong-term&short-termschedulersIIIProcessescanbedescribedaseither:I/O-boundprocessIspendsmoretimedoingI/Othancomputations,manyshortCPUburstsCPU-boundprocessIspendsmoretimedoingcomputations;fewverylongCPUburstsIIMPORTANTforlong-termscheduler:IAgoodprocessmixofI/O-bound

8、andCP